The field of the present invention is thermal processors and stocking systems for semiconductor articles for such processors.
In the processing of semiconductor articles such as wafers, it is often desirable to place the wafers in a furnace for high temperature treatment. Such furnaces typically include a mechanism whereby wafers are stacked in a spaced array in order that the surfaces of each wafer are exposed to the reactive gases within the furnace.
One such furnace includes a base of circular construction upon which a pedestal is placed. An article support extends upwardly from the pedestal to receive a column of horizontally disposed and vertically displaced wafers. The wafers are supported only on the outer edges. A process container which is typically a quartz cylinder and dome may be lowered about the column into a sealing arrangement with the base. A furnace heating element assembly is then lowered about the process container until it too rests on the base. The process container and the furnace heating element assembly may be raised and lowered by independent lifts which can be, for example, pneumatic cylinders.
With such furnaces, a furnace housing is provided which encloses the entire furnace mechanism and provides a very clean environment. Within the furnace housing, in addition to the furnace, two further article supports may be provided to receive wafers in the same orientation as the furnace itself, defining a preload station and a cooling station. The first column of wafers is typically to accommodate a full furnace charge of unprocessed wafers while the second column of wafers receives the same quantity of already processed wafers. A robot having a semiconductor wafer end effector is included within the furnace housing. The robot with the end effector is able to extend to an indexer port where pods of wafers are presented. The end effector moves individual wafers from such a pod to the first column of wafers within the furnace housing. The same end effector is also able to extend to the article support within the furnace to both load and unload individual wafers therefrom. Further, it can extend to the second of the article supports in the furnace housing in order that the furnace may be unloaded, the wafers cooled and ultimately the wafers replaced into a pod at the loadport.
In operation, a pod of approximately twenty-five wafers is positioned at the loadport. These wafers are moved one at a time by the end effector and placed in the preload wafer column. Completed wafers may be unloaded from the cooling wafer column by placing them back in a waiting pod at the indexer port. The process of both loading the furnace housing from the pods and loading the pods from the furnace housing may be accomplished during a furnace cycle when the process container and furnace heating element assembly have been brought down onto the base and heated according to a preset thermal cycle.
The pods are of known construction. In the case of 200 mm. wafers, the pods tend to be defined by a base with a cover. The cover is locked to the base and extends outwardly around the base as well. Indexers are available for pods accommodating 200 mm. wafers which automatically unlock the base from the cover and lower the base from beneath the cover for access to the wafers. In a 300 mm. pod, a door is provided on one side of the pod. The door may be unlocked and removed for access to the wafers within. As the pods typically do not include a full charge for the furnace, multiple pods must be positioned for the wafer end effector to unload to the preload station or load from the cooling station. The pods are then resealed and locked for transportation to storage or a further process.
The loading or unloading of one pod may take approximately ten minutes to accomplish. Time is available during the heating cycle when preparatory tasks might be conducted. To create a most efficient use of the furnace time for both loading and unloading between heating cycles, the columns within the furnace housing for incoming and outgoing wafers can be appropriately charged from and discharged to the pods during the thermal furnace cycle. This maximizes the efficiency of the loading and unloading process. Even so, it is disadvantageous to require manual loading of the furnace where attention must be directed to the furnace approximately every ten minutes. Consequently, the possibility has been known to provide a work-in-progress stocker for storing wafers in pods on a more rapid basis in a clean environment for later automatic delivery to the loadport of the furnace housing.